When used in solid-liquid and liquid-liquid separation applications filters serve a critical function to ensure process quality and repeatability. Whether it could remove the particulates that can damage equipment or remove water from fuel to extend system service life is very important. Improper filter design and filter media selection can result in catastrophic failure.

The concept that filters have a specific "DNA" may seem odd but just as Deoxyribonucleic Acid ("DNA') defines the nature of the human body, there is a "DNA" associated with a filter that defines how it will perform. Filters are used to separate many different particles and liquids. The effectiveness and efficiency of filters can be determined by laboratory testing before expensive plant modifications are made for real world use. For instance, most filters and filter media have an "unloading point" that is a measureable differential pressure at which filters release trapped contaminants downstream. The correct testing can find these "unloading points". These released downstream particulates can erode or ruin an engine, cause scrap in food and beverage processing, or may even seize mechanical system components. Even before the burst point where the particulates downstream increase, due to change in pressure or other external conditions, can still destroy the system. Each filter has its own attributes and to determine them you need to consider multiple tests to define the "DNA" of a filter.

The testing to determine the "DNA" of a filter is much more inclusive than simple initial efficiency, mean pore flow or bubble point testing techniques. While these provide a good starting point, “DNA” testing is more holistic than the above-mentioned tests that provide only one small detail about the filter. The idea of knowing more about a filter is essential in determining where the filter would perform the best and where it will perform the worst. “DNA” tests using international standards provide results that are repeatable and allow “apple to apple” comparison with other filters and their applications.

The “DNA” of a filter is formed from the results of various tests depending on the process application.

Liquid filter media all have the same role of letting the liquid flow through whilst retaining a part if not all particles in suspension. Liquid filtration occurs in a very broad variety of processes and equipments, from engines fuel or lubricating oil to drinking water through chemicals, blood or varnishes.

Depending on the type of filter used, filtering media are of made of layers of grains (sand or diatomites) or of fibers, which can be wound or processed or papers.

The variety of techniques, processes and liquids they are applied to create a broad spectrum of technical requirements and properties. Tests are developed to evaluate these properties in accelerated conditions, cheaper and much faster than actual operation ones.

The lecture will present an overview of the characteristics of filter media (from granular ones to sterilizing membranes) classified in four families: intrinsical relating to the internal structure of the porous media, hydraulic which cover the impact of the media on the fluid flow, performances, i.e. how the media retains particles or undesirable substances and the impact of their retention on both the permeability and the efficiency and compatibilities, including all “negative” interactions between the media material and the filtered fluid.

Main test procedures (especially standard ones) will be summarised. A brief presentation will be made of their principles, of the equipments and products used, of the criteria of validation of test benches.

The way raw data have to be processed to obtain standard test report will be explained and typical interpretation of data oriented toward the optimisation of the choice of filtering media will be given.